Tuning the Fermi level (EF) in Bi2Te3 topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE).

Ultrathin bilayers (BLs) of bismuth have been predicated to be a two-dimensional (2D) topological insulator. Here we report on a new route to manufacture the high-quality Bi bilayers from a 3D topological insulator, a top-down approach to prepare large-area and well-ordered Bi(111) BL with deliberate hydrogen etching on epitaxial Bi2Se3 films. With scanning tunneling microscopy (STM) and X-ray photoelectron spectra (XPS) in situ, we confirm that the removal of Se from the top of a quintuple layer (QL) is the key factor, leading to a uniform formation of Bi(111) BL in the van der Waals gap between the first and second QL of Bi2Se3. The angle resolved photoemission spectroscopy (ARPES) in situ and complementary density functional theory (DFT) calculations show a giant Rashba splitting with a coupling constant of 4.5 eV Å in the Bi(111) BL on Bi2Se3. Moreover, the thickness of Bi BLs can be tuned by the amount of hydrogen exposure. Our ARPES and DFT study indicated that the Bi hole-like bands increase with increasing the Bi BL thickness. The selective hydrogen etching is a promising route to produce a uniform ultrathin 2D topological insulator (TI) that is useful for fundamental investigations and applications in spintronics and valleytronics.

Tetrahedral symmetric NiO2 and Pd respectively facilitate H2 splitting and CO2 to CO reduction and thus enable an ultra-high CH4 production yield performance in the epitaxial interfaces in the bimetallic NiO2@Pd NPs.

Nitrogen-containing aromatics have potential applications in surface functionalization, corrosion inhibition, and carbon-nitride materials. Reflection− absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and temperatureprogrammed reaction/desorption (TPR/D) have been employed to study the system of 2,4-C 5 NH 3 Br 2 /Cu(100). Our experimental results indicate that 2,4-C 5 NH 3 Br 2 is adsorbed predominantly in molecular form on Cu(100) at 100 K; however, a tiny fraction of the adsorbed molecules is subjected to debromination. The 2,4-C 5 NH 3 Br 2 undergoes partial C−Br dissociation below 400 K, forming C 5 NH 3 Br intermediate. Although after breaking both the C−Br bonds (>400 K), 2,4-pyridyne (C 5 NH 3 ) can be formed, the possibility of Ullmann coupling reaction cannot be excluded. The NEXFAS study shows a ∼ 35°average inclination of the aromatic plane, with respect to the surface, in a packed 2,4-pyridyne adsorption layer. Thermal decomposition of the C 5 NH 3 or its coupling reaction products on the Br/Cu(100) surface mainly occurs at a temperature higher than 550 K, generating H 2 , HCN, HBr, and (CN) 2 .

By taking advantage of the similarity between pentacene (PEN) and anthradithiophene (ADT) in molecular dimension and charge transport property, we have produced organic field-effect transistors (OFETs) with active layers consisting of well-blended PEN/ADT films. The blend-films were characterized by atomic force microscopy, X-ray diffraction, and soft X-ray spectroscopies. It is found that the blend-films containing no more than 10% of ADT exhibit a single-phase structure, large crystallinity, and improved oxidation resistance, as compared to PEN. The best performance achieved with 90% PEN-OFET gives a mobility of 0.37 cm2 V–1 s–1 and an on/off current ratio of 107. More importantly, this device provides a 3-fold improvement in operational stability as well as extended environmental stability. After the repetitive scanning between on and off states of OFET in ambient 940 times, the mobility decreases only to 0.33 cm2 V–1 s–1. In comparison, the mobility of PEN-OFET decreases from 0.46 to 0.22 cm2 V–1 s–1. After 3-month storage in ambient, the mobility of the optimal device decreases to 0.1 cm2 V–1 s–1, whereas PEN-OFET almost loses its mobility.